The present invention relates generally to the field of internal combustion engines and fuel systems therefor, and more specifically to engines operated under homogenous charge compression ignition principles.
It has been known for many years to use spark ignition, or direct injection ignition concepts in internal combustion engines. In the spark ignition design, a mixture of fuel and air is introduced into a combustion cylinder and compressed. A spark plug initiates combustion through the creation of an open spark sufficient to ignite the air and fuel mixture in the cylinder. In direct injection ignition engines, fuel is injected into the already compressed combustion air in the combustion chamber. The heat generated in the compressed air during compression, causes the fuel to ignite. Both two and four stroke operating sequences are known for each spark ignition and direct injection ignition engines.
Increasingly restrictive engine emission standards have led to the investigation of engine operating and compression ignition alternatives. In one such alternative, referred to as homogenous charge compression ignition (HCCI), significant emission reductions have been experienced during initial testing. In an engine operating under HCCI concepts, the fuel is introduced into the cylinder earlier in the compression cycle than for a direct injection ignition engine. The air and fuel are intimately mixed, typically at a high air/fuel ratio, before maximum compression in the combustion cylinder. As a result, each droplet of fuel is surrounded by an excess amount of combustion air, as much as twice the air required for combustion, supporting more complete combustion of the fuel. As compression occurs, the air temperature increases, and ultimately combustion is initiated at numerous locations throughout the cylinder, as the fuel droplets auto-ignite from the heat of the surrounding air. Typically, combustion commences at lower temperatures than for direct charge ignition, leading to reduced NOx emissions.
The use of homogenous charge compression ignition concepts has apparent benefits in substantial reduction of NOx emissions. However, difficulties have been encountered in implementing the HCCI concepts. Fuel preparation is important for peak operating performance of an HCCI engine. The air/fuel mixture must be intimately and thoroughly mixed. Preferably, fuel breakup occurs early in the compression cycle, allowing for intimate mixture of the air and fuel. It is desirable to create droplets of fuel as small as possible in a combustion cylinder operating under HCCI concepts. High pressure injection of the fuel can be used to create surface instabilities on the fuel droplets, causing the fuel spray to breakup and disperse. However, the effectiveness of high pressure fuel injection in creating the smallest possible fuel droplets has been somewhat limited.
It is known to use ultrasonic vibrators in fuel supply systems to atomize fuel prior to introduction of the fuel into a combustion chamber. Commonly, such systems employ chambers or devices for atomizing fuel upstream of the combustion chamber.
U.S. Pat. No. 3,977,608 entitled, xe2x80x9cFuel Injection Nozzle Assemblyxe2x80x9d discloses a fuel injection nozzle having an egg-shaped housing, with a disc shaped ultrasonic vibrator facing auxiliary nozzles, and a ring-shaped vibrator at the throat of the main jet nozzle. The nozzle assembly is capable of atomizing a variety of fuels, oxidizers and water prior to introduction of the fluids to the combustion chamber.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine is provided with an engine block defining therein a combustion cylinder, and a primary piston disposed in the combustion cylinder. A piezoelectric oscillator is disposed in the cylinder. The piezoelectric oscillator is connected to a voltage source.
In another aspect of the invention, a method for operating an engine is provided with steps of providing a combustion cylinder having a cylinder head at an end thereof and a primary piston reciprocally disposed in the combustion cylinder, defining a combustion chamber; providing a piezoelectric oscillator in the combustion chamber; introducing fuel into the combustion chamber; activating the piezoelectric oscillator and initiating waves of ultrasonic energy through the combustion chamber and the fuel in the combustion chamber; dispersing the fuel throughout the combustion chamber; and compressing the fuel in the combustion chamber.
In a further aspect of the invention, a work machine is provided with a machine frame and an engine carried by the machine frame. The engine includes an engine block defining therein a combustion cylinder, a primary piston disposed in the combustion cylinder, and a cylinder head defining an end of the combustion cylinder. The cylinder head defines a secondary cylinder in flow communication with the combustion cylinder. A secondary piston is reciprocally disposed in the secondary cylinder. A piezoelectric oscillator is disposed in the combustion chamber.